This invention relates to hydraulic spool valves of the type utilized in off-highway equipment, as, for example, front-end loaders. Typically, an operator of such a vehicle manually controls an actuator lever adapted to move a cylindrical spool reciprocally within a spool valve. In most cases, the physical forces required to move the spool tend to vary as a function of the throttling or control cycle of the valve. Ideally, such valves would be force balanced, and hence have no unbalanced control forces against which an operator would need to exert himself.
Much design work has been directed to lowering of shift effort required to move hydraulic spools back and forth within spool valve bodies. Many devices attempt to transform the axial flow components normally entering a spool valve body into radial components for the purpose of alleviating or reducing axial pressures on the spool. Although relatively satisfactory in most instances, this approach lacks consistency in results. Moreover, to the extent that the typical system remains susceptible to hydraulic shock loading, it is desirable that any unbalanced component forces are as small as possible.